settle
厎 centers on bringing something to a stable, settled state. The given meaning "settle" captures the idea of resolving or fixing something in place.
厎 combines 厂 (cliff or enclosure) with 氐, which likely contributes the sound and may relate to the idea of a base or foundation, suggesting settling something firmly.
The outer 厂 is like a shelter or enclosure, and inside is 氐, which looks like a person settling down. Picture someone finding a sheltered spot and settling in for the night.
For シ, imagine a person settling into a soft seat: the "sh" sound of settling into the seat cues シ.